Synthesis and physical properties of closothiadodecaborane derivatives
Introduction
At first glance, boron stands humbly in the second row of
Mendeleev's periodic table, at a side of carbon. At second glance,
however, from just any point of view, it remarkably stands out[1]:
Even the origin of this element differs from that of the most of
the others—in the sequence of the thermonuclear element
transmutations inside the stars boron is missing. It is formed in
the interstellar space through the so called X-process. The
element in its standalone form not only belongs to the small group
of metalloids, instead of the larger ones of metals or nonmetals,
but also crystallizes its own unique way, having the atoms grouped
into icosahedrons. The structural element of icosahedron appears
in many boron compounds too, such as in many metal borides, and
especially in the vastest and the most interesting class of its
compounds, boron hydrides.
The hydrides of boron were not only unknown to mankind until the
modern ages, they were virtually nonexistent. Just like silicon,
boron forms very strong, energetically favoured bonds with oxygen
and fluorine, thus in the oxygen rich environment of the Earth—and
probably just any other planet containing more than the first row
elements—it is found only in the form of its oxo-compounds,
borates. The first hydrides of boron on the Earth were prepared at
the end of the nineteenth century[2], but even then their
structure and structural variability had to wait to be recognized
until the first quarter of the twentieth century, when Stock
prepared and identified a lot of them in his pioneering work on
the hydrides of boron and silicon[3]. And then the mysteries of
boron hydrides structures did not end, but, on the contrary,
began.
Out of naïve stoichiometric considerations we would expect the
lowest, simplest boron hydride to be borane, BH3. Nevertheless such
a compound does not exist—a particle of this constitution has been
identified as a reactive intermediate of many chemical reactions,
but stable as a chemical individuum it definitely isn't. The
better part of the BH3 non-existence is the name borane remains
B
B
Fig. 1: Structure of diborane
free for labelling of the entire class of compounds. The real
lowest borane, diborane, B2H6, puzzled chemists for a long time
since Stock first prepared it in 1912[4] and identified its
1
stoichiometry.
Its doubly bridged structure (Fig. 1), first
B
B
B
B
B
Fig. 2: Structure of pentaborane
proposed by Dilthey in 1921[5], was in a dispute, until Hedberg
and Schomaker finally established it as proven by electron
diffraction measurements in 1951[6]. By then, Brown and co-workers
have discovered utility of B2H6 as a reduction reagent in organic
synthesis[7], and new routes to many compounds, first identified
by Stock[3] in traces, have been opened, thanks to military needs
during the World War II (search for volatile uranium compounds and
for utile means of field hydrogen generation) fuelling
explorations of Brown, Schlesinger et al. on diborane[8][9],
LiBH4[10] and NaBH4[11] production and application[12]. Thus modern
diffractographic methods could be used on variety of boranes and
more amazing structures revealed, such as that of B10H14[13] or
B5H9[14][15][16] (Fig. 2). Growing number of known molecular
geometries helped to develop the theory of bonding in boranes, so
the theorists were prepared, when another wave of military
interest, that time for high performance rocket fuels[17], allowed
chemists to develop the chemistry of boron hydrides[18]. Thus one
of the most stable—if not entirely the most stable one—boronhydrogen compounds, the highly symmetric icosahedral
dodecaborate(12) dianion, B12H122- (Fig. 3), was not experimentally
reported[19], and subsequently synthesized in significant
amount[20][21], before it was theoretically foretold[22].
B
B
B
B
B
B
B
B
B
B
B
B
Fig. 3: Structure of B12H122The ability to foretell new boron hydrides crowned long years of
theoretical struggle with borane structure. Not before about the
2
same time it was definitively corroborated was the doubly bridged
geometry of diborane elucidated from the electronic point of view,
by the concept of the three centre two electron bond proposed by
Longuet-Higgins[23][24], and lately developed and applied to all
the boranes by Lipscomb and co-workers[25]. This concept marked a
major breakthrough in the theory of chemical bond.
The concept of three centre two electron bond allowed Lipscomb to
catalogue then known boranes, depict their structures, and predict
structures of compounds yet unknown. The famous styx—concept deals
with the number of bridging hydrogens (three centre bonds between
two borons and a hydrogen) labelled s, the number of three centre
bonds among borons marked as t, the number of simple boron—boron
bonds in the borane molecule denoted y, and the number of BH2
groups marked as x. Within the framework of the theory of
molecular orbitals as a combination of atomic orbitals (MO-LCAO),
some structural aspects of boron hydrides can be deduced from
their stoichiometric formula and the respective numbers of
electrons and atomic orbitals. Simple—once discovered[25][26]—
electron counting for a borane of BpHp+qz formula (where there are p
B—H bonds in addition to those described by the styx symbols)
reads:
N el=−z4pq =2s2t2y2x2p
−z2pq =2s2t2y2x
which after subtraction of the relation implied by the number of
hydrogen atoms:
N H =p q =sx p
q =sx
leads to:
−z2p=s2t2yx
Since the number of valence orbitals available for bonds formation
is:
N orb=4pp q
=5pq
and the bonds consume:
N orb =3s3t2y2x2p
the orbitals balance results in:
3pq =3s3t2y2x
3p=2s3t2yx
Thus the structure of BpHp+qz molecule is bound to satisfy relations:
s x =q
s2t2yx=2p−z
2s3t2yx=3p
that may be linearly transformed to, for example:
3
sx=q
zq
ty = p−
2
st=p z
For example diborane(6), B2H6, can only have a structure, for
which:
s x =4
ty =0
st=2
and thus, styx having to be natural numbers only, t=0, y=0, s=2,
and x=2. Having styx 0022, we can easily draw the structural
formula of diborane (Fig. 4).
H
H
H
B
B
H
H
H
Fig. 4: the formula of B2H6
The same way we may find for decaborane(14), B10H14:
sx =4
ty =8
st=10
Here t must not be greater than 8, and s cannot exceed 4, which
allows three styx combinations: 2802, 3711, and 4620. Now we see
that even styx determination is ambiguous, to say nothing of the
H
H
H
B
BH
H
BH
BH
BH
BH
BH
B
H
H
H
H
BH
BH
BH
BH
H
BH
B
BH
BH
H
BH
BH
H
H
2802
3711
BH BH
BH
BH
BH
BH
H
BH
BH
BH
BH
H
BH
H
BH
4620
Fig. 5: various structures theoretically possible for B10H14
resulting structural formula (Fig. 5). In straight analogy with
hydrocarbons, the same stoichiometry of boranes can be realized by
different structures; contrary to hydrocarbons, however, among the
boranes actually synthesized so far isomers are rare, most of
known boranes prefer unique geometry, and the only ambiguities in
most of cases consist only of theoretical doubts, which formula,
H
BH
BH
BH
BH BH
H
BH
BH
H
BH
H
BH
BH
4620
Fig. 6: usual structural formula of decaborane
4
or possibly group of resonance formulae, describes best the
electronic state. For B10H14 the right styx is, according to its
determined structure[13], 4620; the most widely used structural
B
+
B
-
B
BB
B
open
closed
Fig. 7: open and closed three centre
bond orbital overlap
formula is shown in Fig. 6. That formula contains two open threecentre BBB bonds—in terms of MO-LCAO bonding overlap of boron
atomic orbitals may happen two ways: as three spn-type orbitals
meeting in the middle of the triangle formed by the bonded atoms
(closed three-centre bond), and as one p-type orbital of one boron
atom overlapping at each side of the atom with an spn-type orbital
of another atom (open three-centre bond), see Fig. 7.
Presently, the open type of three-centre bond is prevalently
regarded as non-existent[27], the importance of the question of
its existence, however, is low, since higher boranes, such as
decaborane, are better described as clusters with much more
extensive delocalization of electrons than structures with
discrete bonds, two or three centre[1]. The first quantum chemical
calculations were done on clusters of high symmetry, at first
octahedral B6H62- and B12H122-[22], using extended Hückel method. The
results, afterwards refined by more subtle and exact calculations
and extended to other compounds of BnHn stoichiometry[28][29],
showed that generally all borohydride clusters of such formula
form n+1 bonding orbitals, n of them being approximately localized
on the cluster surface, and one, the lowest of them all, residing
inside. This gave rise to the concept of spatial aromaticity[30]
[31] and to many questions of the nature of aromaticity, its
possible types and available criterions to discern aromaticity and
antiaromaticity, which are of interest for theorists till present
days[32].
The compact BnHn2- clusters, called closo-boranes (or rather closoborates to stress out their negative charge), were taken by Wade
as the base for his electron counting rules[33]. Not counting the
external B-H bonds to the cluster itself, the closo-species of n
skeletal atoms must have 2n+2 cage electrons. After formal
removing of one apex of the polyhedron, the orbital structure of
the cage may remain roughly intact, especially if we substitute
for the absent three orbitals of boron three hydrogen atoms; thus
we get more open structure with n-1 apices and, counting every
added hydrogen, either as a hydrogen bridge or the second hydrogen
atom of a BH2 group, to the cluster, 2n+2, i. e. 2(n-1)+4
electrons. Such boranes, having n apices and 2n+4 cage electrons,
are called nido. Usually nido-boranes posses formulae BnHn+4 and are
neutral, since the open structure allows for proton incorporation
to compensate for the negative charge; what happens to the cluster
5
orbital structure is a question to be solved by exact quantum
chemistry calculations, but for approximate picture we may call to
help the concept of localized bonds and imagine simple change of a
B-B classical two centre two electron bond to a hydrogen bridge.
Actually such conversion exists as a real chemical reaction, the
bridging hydrogens in boranes are weakly acidic and can be taken
off to produce respective anions.
The bigger the cluster is, the better we may apply formal apex
removal to nido-compounds to further open their structure into
arachno-species, having for n apices 2n+6 cage electrons and
neutral formulae BnHn+6, and they can be open yet further into BnHn+8
hypho-compounds containing 2n+8 cage electrons. As we can see,
change of a borane of one class to another, according to Wade
rules, can be realized not only by a vertex abstraction, but also
as a reduction of the cluster[34]. Both ways of conversion, in
both directions, actually exist in many cases as real chemical
reactions too[35][36].
Of course, the catalogization of highly open, loosely connected
structures, for which the concept of a cluster is dubious, may
become rather formal, and sometimes, in case of various boron
hydrides derivatives, questions of what belongs to the cage and
what substitutes it, resulting for example in problems with
correct atom numbering, are raised[37]. Thus, the two basic
approaches to boron hydrides structures, molecular orbitals for
tight clusters and localized bonds for loose nets, are
complementar[38]. Nevertheless the closo, nido, arachno, and hypho
classification proved to be plausible, the classes of boranes
differing in their reactivity, the span of their NMR spectra and
so on, and Wade rules of electron counting very useful. Especially
useful they are to classify heteroboranes—compounds formally
derived from boranes by so called isolobal[39] substitution.
If we take off a B-H vertex of a borane, and instead of it insert
another atom or group contributing the same number of electrons
(2) and the same number of frontier orbitals with equivalent
symmetries, the structure of the cluster may change only little.
Thus substitution of a [C-H]+ for a B-H group, for example, renders
carbaboranes, usually called shortly carboranes[40]. Especially
the mono and dicarba derivatives of the highly stable and highly
symmetric icosahedral closo-B12H122-, closo-CB11H12- and three isomeric
neutral closo-C2B10H12 are well known and of interesting
applications, but a lot of carboranes of all the cluster classes
have been synthesized and up to hexacarba species are known[41].
Nitrogen or phosphorus are isolobal with [B-H-] or C-H as (formal)
[N-H]2+ and [P-H]2+ groups, contributing two electrons to the cage,
and both aza and phospha boranes, with B-H vertices formally
substituted by [N-H]2+ and [P-H]2+ are known[42][43]. Phosphorus,
due to its weaker electronegativity and greater polarizability is
more capable of incorporation into boron clusters, forming various
phosphaboranes or phosphacarbaboranes, in contrast to nitrogen
also as formal P+ with one lonely electron pair[43]. Oxygen, due to
6
its high electronegativity and strong affinity to boron is rare in
the boron clusters, but less electronegative and more polarizable
sulphur is capable of incorporating itself into borane clusters
with one lonely electron pair as a formal S2+ ion, thus forming
various thiaboranes[44][45][46][47], the most symmetric of them
being closo-thiadodecaborane, SB11H11[48], possessing C5v symmetry.
Formally cationic groups isolobal with a B-H apex give raise to
interesting electronic situation, especially in cases of atoms
more electronegative than boron—i. e. in almost every case other
than metallaboranes. Atoms, that in simple classical bonding
situation would attract electrons from boron, are forced in
clusters to contribute their electrons to the inner bonding
orbital shared all over the cluster, thus retaining only small
part of them. In icosahedral carboranes, for example, each carbon
atom contributes one electron into that orbital, getting back only
one twelveth share of its electron pair, i. e. 1/6 of electron.
This must result in distortion of the cluster electronic structure
with respect to the isostructural borohydride, the inner orbital
being shifted to carbon, and the electrons in the surface orbitals
being dragged from borons to carbon. Thus the boron atoms next to
carbon are rendered positive in comparison with the further placed
borons, and for example in closo-1,2-C2B10H12 nucleofilic attack at
the boron 3, neighbouring with both carbons, is well known to lead
to boron vertex abstraction. However, the loss of 5/6 of electron
is so big, that it is not entirely compensated for, and the carbon
atoms in carboranes are slightly positive too, as is manifested in
acidic character of their hydrogens[40].
The situation of sulphur, especially in closo-thiadodecaborane, is
yet more pronounced, the quite strongly electronegative sulphur
losing 15/6 electrons to the inner bonding orbital. Compensating
for so a big electron loss by the sulphur atom induction effect is
as unimaginable as the other possibility, the possibility of
positive sulphur atom bonded to nothing more electronegative than
boron. The existence of closo-SB11H11 is unquestionable, since the
compound have been synthesized. Thus other questions remain: Is
sulphur really the most positive spot in the molecule, as we can
guess from naïve consideration of the cluster orbital structure?
What effect may that have on the neighbouring borons? How is the
electric charge distributed in the molecule, how does its
distribution manifest itself in the properties of
thiadodecaborane, and how does it interact with possible
substituents on the cluster? The high symmetry of the species can
aid to looking for answers to such questions.
7
The state of the art
closo-thiadodecaborane synthesis
The first derivative of closo-SB11H11 to appear was 2-Ph-SB11H11 in
1967[44], synthesized by Hertler, Klanberg, and Muetterties
through vertex addition to nido-7-SB10H12:
7-SB10H12
BuLi
Ph-BCl2
THF
2-Ph-SB11H10
The synthesis of the parent thiadodecaborane was accomplished by
Plešek and Heřmánek eight years later[48]:
7-SB10H12 + Et3N·BH3
SB11H11 + Et3NH+SB10H11- +Et3N
Δ
38%
≈50%
Parallel research, published yet one year later by Pretzer and
Rudolph[45], revealed among others an alternative way to closoSB11H11 by pyrolysis of nido-7-SB10H12, but only in 4% yield, the
former cage expansion thus being highly preferable.
Hertler, Klanberg, and Muetterties described[44] two step route to
nido-7-SB10H12: nido decaborane, one of the basic raw materials of
boron hydrides chemistry, was converted by amonium polysulfide
into arachno-6-SB9H12-,
B10H14 + (NH4)2Sn
-B(OH)4-, -H2
H2O
6-SB9H12- CsCl
Cs(6-SB9H12)
and arachno-thiadecaborate then pyrolysed in the form of cesium
salt to produce nido-7-SB10H12 in about 50% yield to the starting
B10H14.
Δ
Cs(6-SB9H12)
Cs(7-SB10H11) HCl
7-SB10H12
In the same paper the authors reported oxidation of arachnothiadecaborate in acetonitrile to the respective adduct of nidothiadecaborane, arachno-9-acetonitrile-6-thiadecaborane,
Cs(6-SB9H12)
I2
CH3CN
9-(CH3CN)-6-SB9H11
and vertex addition to this adduct under influence of
triethylamine-borane to produce triethylammonium nidothiaundecaborate.
9-(CH3CN)-6-SB9H11
Et3N∙BH3
Δ
[Et3NH][7-SB10H11]
They, however, regard the pyrolytic way as preferable.
Pretzer and Rudolph in their work from 1976[45] modified the
oxidation of Cs(SB9H12) exchanging electron donor acetonitrile in
the role of solvent for non-donor benzene. That way they obtained
nido-SB9H11 in good yield.
Cs(6-SB9H12)
I2
benzene
6-SB9H11
This allowed Kang and Sneddon in 1988[49] to start their improved
way to nido-SB10H12 from nido-SB9H11. They augmented its skeleton
either by reaction of neutral nido-thiadecaborane with NaBH4 in
8
dioxane or tetrahydrofuran,
NaBH , Δ
4
6-SB9H11 dioxane
7-SB10H12
or THF
either by acting of BH3•THF in tetrahydrofuran on nidothiadecaborate dianion.
6-SB9H11
NaH
THF
BH3∙THF
Δ
7-SB10H12
Thus closo-thiadodecaborane is relatively easily accessible from
decaborane.
Its derivative chemistry was not subject to great interest, only
several basic observation and studies were done. Plešek and
Heřmánek[48] reported their synthesised SB11H11 to react with
bromine in presence of AlBr3 (generated in situ from aluminium
powder),
SB11H11
Br2/AlBr3
CH2Cl2
12-Br-SB11H10
and Pretzer and Rudolph[45] attempted cage degradation with
ethanolic potassium hydroxide in straight analogy to basic
degradation of 1,2-C2B10H12 with KOH in methanol discovered by
Hawthorne et al.[35].
SB11H11
KOH
C2H5OH
7-SB10H11-
Similar reaction with methanolic sodium hydroxide was used already
by Hertler, Klanberg, and Muetterties[44] to convert 12-Ph-SB11H10
into phenyl-substituted anion, which they in turn reacted with PhBCl2 to obtain diphenyl-closo-thiadodecaborane;
NaOH
BuLi
Ph-BCl
2
2,y-Ph2-SB11H9
2-Ph-SB11H11 CH OH x-Ph-7-SB10H10THF
3
the question of regioselectivity of this synthesis or isomeric
composition of the product was not dealt with in their paper.
In 1977 Smith et al.[50] studied halogenations of closothiadecaborane and closo-thiadodecaborane. They iodinated both
thiaboranes by standing several days at elevated temperature in a
sealed tube with iodine without solvent or catalyst. Bromination
of closo-SB9H9 they achieved through action of liquid bromine on
the parent thiaborane in a vacuum apparatus, examining the same
reaction of SB11H11 by GC separation of the products, since
thiadecaborane contained one percent of thiadodecaborane impurity;
letting SB9H9 stand at room temperature in CCl4 with bromine and
AlCl3 they observed only small degree of conversion. Reaction in
solution they used successfully only for chlorination—on several
hours standing in sealed tube with chlorine and AlCl3 in CH2Cl2 at
room temperature SB11H11 gave 7-Cl-SB11H10, which could be isomerized
by heating to an equilibrium mixture of 7- and 12-isomers. All the
halogenation reactions tended to proceed to higher degrees,
although the thiaboranes were matched to the respective halogens
in 1:1 ratio.
9
closo-thiadodecaborane structure
S
6
2
3
5
4
11
7
9
8
10
12
Fig. 8: closo-thiadodecaborane
molecule
The structure of closo-SB11H11 was studied by the means of electron
diffraction[51]. During making of this work, another structure,
obtained by microwave spectroscopy, was published[52]. Both
results confirm the expected C5v symmetry of the molecule, and are
in good agreement with each other (Table 1), the biggest
difference being in the B3-B7 bond length (the bond connecting the
upper and lower pentagons), equal to 3.5 pm, i. e. 2%.
bonds and
angles
S-B [Å]
B2-B3 [Å]
B3-B7 [Å]
B7-B8 [Å]
B7-B12 [Å]
B-H (mean) [Å]
S—B—H [°]
B12—B7—H [°]
electron
diffraction
2.010(5)
1.905(4)
1.783(8)
1.780(11)
1.777(6)
1.190(3)
120.3(40)
125.3(45)
microwave
spectra
2.013(2)
1.889(1)
1.748(2)
1.797(1)
1.791(3)
n/a
n/a
n/a
Table 1: Experimental structure parameters of SB11H11
The high symmetry makes closo-thiadodecaborane a good model
compound for studies of the substituent effects if symmetrical
substitution (i. e. in the 12 position) is achieved. Then the
number of symmetrically distinct vertices in the polyhedron does
not exceed the number of distinct positions in the benzene
molecule, the classical subject of electron distribution and
substituent effects in organic chemistry.
NMR spectroscopy of boranes
The NMR spectroscopy of boranes and their derivatives was reviewed
by Heřmánek[34]. It is usually the tool of choice for
identification and structure determination of boranes, since its
applicable to most of them (if only they are soluble in some kind
of deuterated solvent and are not paramagnetic), requires
relatively small amounts of species, is non-destructive,
relatively quick, allows for handling of sensitive and volatile
10
substances, and produces vast amount of information (especially
when multidimensional methods are involved). The fact that both
natural isotopes of boron, 10B and 11B, have non-zero nuclear spin,
the prevalent 11B being the more suitable for NMR measurements,
gives NMR spectroscopy in boron hydrides chemistry even better
prospects then in organic chemistry, dealing with zero-spin 12C and
its minor NMR-active 13C isotope. The advantage of boron over
carbon NMR is somewhat lowered due to the quadrupole moment of
both boron nuclei, which promotes relaxation of boron spins, thus
shortening relaxation times, but widening the lines in the
spectra. Also spin-spin coupling between proton and boron lowers
legibility of 1H NMR spectra of boranes without decoupling applied,
especially due to high spins of boron nuclei, 3/2 for 11B and 3 for
10
B, splitting hydrogen lines into quartets and septets
respectively. Finally, what makes NMR spectroscopy of boranes
chalenging, are long range effects of structure and electron
distribution in boranes: the interpretation of boranes NMR spectra
posed a lot of problems in the history of boron chemistry, since
the relation between electron density on individual atoms and
their NMR chemical shifts is by no means straightforward, and the
most significant influences of molecular structure on their shifts
are not confined to their nearest neighbourhood.
Various effects have been described[53][54][55][56][57], the most
pronounced and best known of them being the antipodal effect[55]
[56]: Both heteroatoms in the cage, and substituents on the
skeleton influence strongly the opposite atom in the deltahedrons,
as well as in many deltahedral fragments, if the apices in
consideration lie in a plane of molecular symmetry. Their impact
on the opposite—antipodal—atom's chemical reactivity and NMR
behaviour is from a naïve point of view contradictory. The
electron attracting heteroatoms, like carbon, phosphorus or
sulphur, cause the antipodal position being the most reactive
towards electrofilic attack (deactivating all the closer atoms of
the cage more than the furthermost one), but at a time the most
deshielded one. The electron attracting substituents, like
halogens, do not act on the antipodal atom NMR properties in
direct contradiction to their influence on its chemical
reactivity, but their impact on the antipodal NMR chemical shifts
is much large than their influence on the reactivity, and opposes
the effect of electron attracting heteroatoms. This behaviour is
explained by asymmetrical electron distribution, and division of
the antipodal atom's orbitals into chemically active and NMR
active ones, only the latter being strongly affected by the
antipodal substitution.
Lately, consideration of 11B—1H coupling constants was suggested[58]
as another source of structural information, possibly related to
the total electron density at the deltahedrons apices or to the
density in the chemically active orbitals. While their dependence
on heteroatoms presence looks promising, the substituent effects
found so far are too small to produce unequivocal results.
11
Experimental section
General procedures
All reactions were carried out under nitrogen atmosphere, using
either baloon with N2, or a standard vacuum line described by
Shriver[59]. During chromatography and other manipulation,
however, the compounds were handled without special protection.
The solvents of analytical grade were purchased from Lachema; the
ethers for reactions with phenylmetallics were dried over sodium
metal and freshly distilled. Chromatography was carried out on
columns of silicagel (Lachema L 100/160; later attempts to use
Aldrich silicagel 230—400 mesh for the halogenderivatives failed,
apparently due to products degradation on more active stationary
phase surface). The purity of individual chromatographic fractions
was checked by analytical TLC on Silufol (silica gel on aluminum
foil; detection by I2 vapor, followed by 2% aqueous AgNO3 spray).
Melting points were determined in sealed capillaries and are
uncorrected. GC/MS and heated inlet MS were measured by Z. Plzák
with Magnum Ion Trap apparatus by Finnigan MAT company, using
electron impact ionization. For basic identification of products
by NMR Varian Inc. Unity 200 equipment at the ground of the
Institute of Organic Chemistry and Biochemistry was used with
switchable broadband probe; better resolved spectra of selected
samples were than obtained by J. Fusek at the same place on
UnityPlus 500 NMR spectrometer from the same manufacturer, using
indirect detection probe.
X-ray diffraction measurements were performed interpreted by
I. Císařová at the Faculty of Natural Sciences of Charles
University, using four-circle diffractometer Nonius KappaCCD
equipped with a CCD area detector. Crystals of 12-Cl-closo-SB11H10
and 12-I-closo-SB11H10 were grown by crystallization from hot
hexane. All the successfully measured phenylderivatives, 2-Phcloso-SB11H10, 2-Ph-12-I-closo-SB11H9, 2-(4-NO2-Ph)-closo-SB11H10, and
2-(2-NO2-Ph)-closo-SB11H10, crystallized from saturated hexane
solutions during prolonged standing. The reflection intensities
for all the compounds were collected. The crystals were mounted on
glass fibbers with epoxy cement and measured at 150(2)K with MoKα
radiation (λ = 0.71069 Å, graphite monochromated). The structure
was solved by the direct method (SIR97)[60] and refined by a full
matrix least squares procedure based on F2 (SHELXL97)[61] . All
non-hydrogen atoms were refined with anisotropic temperature
factors. The hydrogen atoms of the thiaborane cage were located on
difference Fourier maps and refined isotropically.
Dipole moments were determined by Všetečka at 25 °C in benzene
12
(usually five solutions, weight fractions from 2.0x10-4 to
1.2x10-3). Relative permitivities were measured at 6 MHz on homemade equipment[62] with direct frequency reading. For refractive
indices measurements Aerograph Refractive Index Detector (Varian)
was used. The dipole moments were obtained by extrapolation to
infinite dilution according to the method of Guggenheim[63] and
Smith[64].
Quantum chemical calculations were performed on the Power
Challenge XL computer of the Supercomputing Center of the Charles
University in Prague. Quantum chemical package Gaussian 94[65] was
used. Geometries were optimized on the MP2[66] level of theory,
using 6-31G* basis[67][68][69][70] (inner orbitals represented as
contractions of six primitive gaussian, valence orbitals as pairs
of two independent functions, one of them being contracted from
three gaussians, and all the non-hydrogen atoms bases augmented by
a polarisation orbitals, i. e. orbitals with higher angular
momentum, than is the highest one for the valence shell); for
heavier halogens (Br, I) attempt to account partially for
relativistic effects was made by usage of double zeta polarisation
basis (DZP) with Stuttgart energy consistent pseudopotentials
fitted to Wood-Boring quasirelativistic calculations of neutral
atoms (ECP-MWB)[71]. NMR chemical shifts were subsequently
calculated at the Hartree-Fock[72] level of theory using the GIAO
(gauge-invariant atomic orbitals) approach[73][74][75], both in
the same basis and with 6-31G* substituted by IGLO II[76] basis.
For comparison, DFT[77] calculations were carried out using
Becke's three parameters hybrid functional[78] with the
correlation functional of Lee, Young and Parr[79] (B3LYP); for all
atoms up to Cl 6-31G* basis set was used during geometry
optimization and IGLO II in GIAO calculations of the NMR paramers,
while DZP/ECP-MWB pseudopotential basis set was applied to Br and
I. Attribution of the discrepancies in the results for molecules
with Br and I to the spin-orbital (SO) coupling was proved by M.
Kaupp at the Würzburg University by sum over states density
functional perturbation theory (SOS-DFPT)[80][81] calculations
within IGLO (Individual Gauge for Localised Orbitals)[82][83]
frame with deMon[84] quantum chemical package, modified by his
group to account for the SO coupling[85]. Geometries optimized in
Gaussian 94 with MP2 method and 6-31G* basis, substituted on Br and
I by DZP/ECP-MWB, were used, and IGLO II basis with DZP/ECP-MWB on
Br and I applied to the NMR calculations.
closo-thiadodecaborane
closo-thiadodecaborane, closo-SB11H11, was synthesised the way
described by Plešek and Heřmánek 1975[48]. The route from nidodecaborane was furthermore simplified by use of unpublished
results of Holub[86]:
13
B10H14 + 2S + Et3N
- H2S (?)
CHCl3
Et3NH+SB10H11- + Et3NH+SB9H12-
starting nido-7-thiaundecaborane was obtained from reaction of
nido-decaborane(14) with sulfur.
The overall procedure was modified according to Plešek[87] to
proceed as a two step one pot synthesis from nido-decaborane,
nido-B10H14.
Colourless crystalline closo-SB11H11 is plasticised to some extend
by impurities which are not detectable by NMR, according to GC/MS
consist probably of some ethyl derivative, and can be removed by
recrystallisation from aliphatic solvents.
Procedure: Typically 5 g (41 mmol) of B10H14 (122.22 g/mol) were
dissolved in 100 ml of CHCl3 and approximately two equivalents—e.
g. 2.8 g (87 mmol)—of sulfur (32.06 g/mol) were added. The
mixture was stirred under nitrogen, and cooled in cold water bath.
Then roughly one equivalent—e. g. 7 ml (50 mmol)—of Et3N (101.19
g/mol, 0.726 g/cm3) was gradually put in and stirring under
nitrogen prolonged for several hours. According to periodical TLC
checks (Silufol, CH3CN + CHCl3 1:1), the decaborane ceased
quickly. After prolenged standing the mixture was evaporated using
rotary vacuum evaporator. Then at least twofold excess—e. g. 13 ml
(88 mmol)—of ET3N·BH3 (115.03 g/mol, 0.777 g/cm3) was added,
mixture placed into a short-path distilation apparatus (based on a
vedge-shaped tube with a termometer and a reflux condenser
adjoined), and heated under nitrogen to 170—190 ºC. Distilate
cummulated, and gases evolved, both suspected to contain poisonous
and flamable lower boranes; progress was marked by white SB11H11
sublimming into higher parts of the reaction bulb or even into the
mouth of the apparatus. The heating continued several hours, as
long as new distilate condensed, and the temperature of the vapor
kept over 40 ºC (althoug the boiling point of triethylamine is
about 78 ºC, the vapor temperature never reached that value, it
kept rather about 60—70 ºC). After cooling the apparatus down, the
resulting yellow sticky plastic substance was dissolved in minimal
amount of CH2Cl2, poured over a small amount of silicagel, and
evaporated. The saturated silica was then placed on the top of a
silicagel column, and SB11H11 (162.07 g/mol) was isolated by
chromatography with isohexane, checking the eluate by TLC (RF≈0.45
on Silufol in isohexane).Optionaly it was afterwards recrystalised
from isohexane. Yields obtained were less than 50%—e. g. 3.0 g
(18.5 mmol), i. e. 45%. RF(hexane)≈0.45; m. p. 329—331 °C; NMR see
Table 6. GC/MS: tret=586 s, m/e=164 [7%] (S11B11H11 M+), 160 [100%]
(from S11B710B4H11 M+ to S11B11H11 [M-4H]+); before recrystalisation
there are about 5% of an impurity, tret=695 s, m/e=192 [3%]
(probably C2H5-S11B11H10 [M-H]+), 188 [100%] (perhaps from C2H5S11B610B5H10 [M]+ to C2H5-S11B11H10 [M-5H]+); 162 [6%] ([S11B11H9]+, i. e.
[M-C2H6]+ or [S11B1010BH10]+, i. e. [M-C2H5]+), and 159 [17%] (probably
from [S11B710B4H10]+ to [S11B11H6]+) among other fragments—probably an
ethyl derivative.
14
12-halogenderivatives of closo-thiadodecaborane
Halogenation was based on the results of Plešek and Heřmánek[48],
and Smith et al.[50].Unfortunately these results were not fully
reproduced. Chorination, simplified to introduce chlorine into the
solution, appeared to produce chlorderivatives well, but in
virtually unseparable mixture of isomers, while bromination in
dichlormethane, speeded up by reflux, ended up as a waste mixture,
GC/MS of which indicated that oligomeration of the solvent and
alkylation of the thiadodecaborane skeleton most probably took
place. Extreme results were obtained with iodine in chloroform in
the presence of AlCl3, when carbonization of the solvent occurred.
While the origin of such complications and their mechanisms were
not successfully elucidated, methods were found to avoid the
problems. Iodination according to Smith et al.[50] would be
impractical, but procedure used by Štíbr et al.[88] for
carboranes, applying benzene as solvent, worked well. Bromination
of solid thiadodecaborane with bromine without solvent, reported
by Smith et al.[50], proved to be useful up to gram scale, and
even tolerant to air, thus not demanding special laboratory
equipment. As a chlorinating agent, tetrachlormethane in presence
of AlCl3[89] did a good job.
Due to the degradation of the skeleton observed in the presence of
fluoride anion, fluorination was not performed.
12-I-closo-1-SB11H10: Closo-thiadodecaborane (0.5 g, 3.1 mmol in
the first experiments, and 1—2 g in the subsequent preparations;
162.07 g/mol) was dissolved in benzene (approximately 20—50 ml),
10% excess of iodine (253.81 g/mol–0.9 g, 3.5 mmol in the first
experiment), and slightly more than one equivalent of AlCl3 (133.34
g/mol–0.5 g, 3.7 mmol) were added, and the mixture was boiled
under reflux. The progress was monitored by thin layer
chromatography on the Silufol silica plates, using isohexane as
the eluent. According to the TLC the reaction was completed in
about two hours—the spot of closo-SB11H11, showing
characteristical diffusion pattern when treated with AgNO3, of
RF≈0.44 on Silufol in pentane, had lessened signifficantly, the
protracting spot of RF≈0.13 in that arrangment, reducing AgNO3,
evolved, apparently belonging to the iodo-derivative, and the
pattern hadn't changed reasonably for a prolonged time period
(about half an hour). Then the reaction mixture was let to cool
down to the room temperature, rinsed two-times with 25 ml of
approximately 5% K2S2O5, and dried with either MgSO4 or Na2SO4.
The dry benzene solution was evaporated on the rotary vacuum
evaporator, and the residuum dissolved in 10—50 ml of an alifatic
solvent such as isohexane, pentane or heptane. Its solubility
appeared, especially in cases of bigger ammounts, to be low, and
dissolved after heating, the 12-I-closo-1-SB11H10 readily
crystalized as long colorless neadles. The dissolved part of the
reaction mixture was separated by column chromatography on 30—50 g
15
of silicagel with the chosen alifatic solvent as the eluent. In
the first experiment (where pentane was chosen and no
crystalization occured) 28% of closo-SB11H11 (0.14 g) was
regenerated, and 12-I-closo-1-SB11H10 (287.97 g/mol) obtained in
73% yield (0.47 g) , considering the amount of closo-SB11H11
consumed. RF(hexane)≈0.14; m. p. 158—160 °C; NMR see Table 6. MS:
m/e=290 [13%] (I-S11B11H10 M+), 288 [41%] (from I-S11B910B2H10 M+ to IS11B11H10 [M-2H]+), 163 [32%] ([S11B11H10]+, i. e. [M-I]+), 161 [100%]
(probably from [S11B910B2H10]+ to [S11B11H8]+).
12-Br-closo-1-SB11H10:Several grams (e. g. 2g, 12.3 mmol) of solid
closo-SB11H11 (162.07 g/mol) was grined and put to a 250 ml bulb. An
excess (e. g. 1 ml, 19.8 g, 124 mmol) of liquid Br2 (159.81 g/mol,
19.78 g/cm3) was poured on it, and the mixture was left untouched
at least one day, although the reaction seemed, producing the
white smoke of HBr, to proceed immediately. Then the mixture was
dissolved in an alifatic hydrocarbon, usually isohexane, checked
with TLC, and separated by chromatography on silicagel (50—100 g)
with the chosen hydrocarbon. In isohexane on Silufol, the
characteristical spot of closo-SB11H11 was seen at RF≈0.49, and a
protracting reducing spot appeared at RF≈0.15, signifying the
formation of 12-Br-closo-1-SB11H10 . This is practically
indistinguishable, especially due to the protracting nature of the
spots of the halogen derivatives, from 12-I-closo-1-SB11H10. Just
like for the iodo-derivative, the crystalization proved to be very
good method for the final purification of the product, as well as
for the preliminary isolation of a partial amount of it, when
working with greater quantities. The flat tablet-like crystals of
12-Br-closo-1-SB11H10 differ conspicuously from the needles of 12I-closo-1-SB11H10 . In the first experiment (starting from 2 g of
closo-SB11H11), 46% (0.92 g) of the starting material were
regenerated, and from the closo-SB11H11 consumed 50% yield (0.80
g) of 12-Br-closo-1-SB11H10 (240.97 g/mol) was obtained.
RF(hexane)≈0.15; m. p. 229—232 °C; NMR see Table 4. GC/MS: tret=800
s (96.2%), m/e=244 [11%] (81Br-S11B11H10 M+), 241 [57%] (from 79BrS11B1010BH10 M+ to 81Br-S11B11H10 [M-3H]+), 163 [30%] ([S11B11H10]+, i. e.
[M-Br]+) 161 [100%] (from [S11B910B2H10]+ to [S11B11H8]+)); tret=885 s
(3.8%), m/e=272 [17%] (probably M+ of 81Br-C2H5-S11B11H9), 269 [78%]
(possibly from [79Br-C2H5-S11B1010BH9]+ to [M-3H]+ of 81Br-C2H5-S11B11H9),
194 [9%] ([M-Br+3H]+?), 191 [34%] ([C2H5-S11B11H9]+ i. e. [M-Br]+), 189
[100%] (probably from [C2H5-S11B910B2H9]+ to [(C2H5-S11B11H9)-2H]+), and
among the others also SB11 cage multiplet with m/e=162 [9%]
([S11B11H9]+ i. e. [M-Br-C2H5]+), 160 [16%] (possibly from [S11B910B2H9]+
to [S11B11H8]+)—probably ethyl-Br-SB11 derivative.
12-Cl-closo-1-SB11H10 + 7-Cl-closo-1-SB11H10 :33 mg of closoSB11H11 were dissolved in 40 ml of CH2Cl2, approximately equimolar
amount of AlCl3 was added, and gaseous Cl2 was being introduced
for several hours. Reaction at the room temperature lead to the
16
mixture directly; no significant changes in its composition were
observed under heating to approximatly 300 ºC, and separation of
the mixture by the means of column chromatography was found
virtually impossible—both isomers have almost the same RF. TLC in
pentane on the Silufol showed RF≈0.46 for closo-SB11H11 and
RF≈0.18 for both 7-Cl-closo-1-SB11H10 and 12-Cl-closo-1-SB11H10.
The spot of the halogen derivatives was protracting, making
differentiation between the isomers even harder. GC/MS: tret=586 s
(5.6%, closo-SB11H11), m/e=164 [7%] (S11B11H11 M+), 160 [100%] (from
S11B710B4H11 M+ to S11B11H11 [M-4H]+); tret=723 s (34.0%, 7-Cl-closo-1SB11H10), m/e=200 [6%] (37Cl-S11B11H10 M+), 195 [100%] (from 37ClS11B610B5H10 and 35Cl-S11B810B3H10 M+ to 37Cl-S11B11H10 [M-5H]+), and among
the fragments m/e=162 [14%] (from [S11B1010BH10]+, i. e. [M-Cl]+, to
[S11B11H9]+, i. e. [M-HCl]+), 160 [39%] (from [S11B810B3H10]+ to
[S11B11H7]+); tret=734 s (60.4%, 12-Cl-closo-1-SB11H10), m/e=200 [8%]
(37Cl-S11B11H10 M+), 196 [100%] (from 37Cl-S11B710B4H10 and 35Cl-S11B910B2H10
M+ to 37Cl-S11B11H10 [M-4H]+), and among the fragments m/e=162 [30%]
(from [S11B1010BH10]+, i. e. [M-Cl]+, to [S11B11H9]+, i. e. [M-HCl]+),
160 [73%] (from [S11B810B3H10]+ to [S11B11H7]+). NMR (11B, 64 MHz; CDCl3,
ambient temperature): δB=22.24 ppm (apparently 1 B of the major
product, s—B12, 12-Cl-isomer), δB=-7.95 ppm (apparently 1 B of the
minor product, d; 1J(11B,1H)=161 Hz—B12, 7-Cl isomer), δB=6.36 ppm
(apparently 1 B of the minor product, s—B7, 7-Cl-isomer), δB=-4.98
ppm (many B, several obscured signals—probably B7-11 of 12-Cl, and
B8-11 of 7-Cl isomer), δB=-8.08 ppm (many B, several obscured
signals—probably B2-6 of 12-Cl, and B2, 3, 4, 6 of 7-Cl isomer),
δB=-13.5 ppm (apparently 1 B of the minor product, d; 1J(11B,1H)=186
Hz—B5, 7-Cl isomer).
12-Cl-closo-1-SB11H10 :0.574 g (3.5 mmol)of closo-SB11H11 (162.07
g/mol) were dissolved in 40 ml of CCl4, 0.481 g (3.6 mmol —
slightly more than equimolar amount) of AlCl3 (133.34 g/mol) were
added, and the mixture was boiled under reflux. It quickly
darkened, and soon TLC showed that closo-SB11H11 completely
ceased, only a protracting reducing spot of RF≈0.14 in isohexane
was indicated. (In another experiment with about 1 g of the
starting material, after 30 minutes of reflux a spot of closoSB11H11 was still observed at RF about 0.43, but no significant
amount of the starting material was regenerated either.) The
mixture was rinsed by approximately equal volume of water (which
may possibly be unnecessary, only washing out the aluminium
chloride), and evaporated with a small amount of silicagel. Then
the product was isolated by column chromatography on approximately
30 grams of silicagel with isohexan. 0.498 g of 12-Cl-closo-1SB11H10 were obtained, the yield being 72%. 12-Cl-closo-1-SB11H10
readily crystalizes from pentane or isohexane, its crystals being
simmilar to those of 12-Br-closo-1-SB11H10. RF(hexane)≈0.15; m. p.
274—276 °C; NMR see Table 5. GC/MS: tret=734 s (with traces of
closo-SB11H11 having tret=586 s), m/e=200 [10%] (37Cl-S11B11H10 M+),
17
196 [100%] (from 37Cl-S11B710B4H10 and 35Cl-S11B910B2H10 M+ to 37Cl-S11B11H10
[M-4H]+), and among the fragments m/e=162 [23%] (from [S11B1010BH10]+,
i. e. [M-Cl]+, to [S11B11H9]+, i. e. [M-HCl]+), 160 [56%] (from
[S11B810B3H10]+ to [S11B11H7]+).
Phenyl derivatives of closo-thiadodecaborane
Phenylation of closo boron compounds is usually achieved by
crosscoupling of their iod derivatives with appropriate
organometallic reagents[90]. In the case of 12-iod-closothiadodecaborane Kumada coupling[91], used successfully by Fox for
carboranes[90], failed. The nature and the reason of this failure
were studied and unexpected reaction found: closothiadodecaborane, both substituted and parent, reacts with
phenylmagnesiumbromide without catalyst to substitute one hydrogen
adjacent to the sulphur atom by the phenyl group; multiple
substitution in one step was not observed, but the possibility of
subsequent phenylation to the second degree was confirmed.
C4
C5
C6
C3
S
2
3
C1
C2
6
5
4
11
7
10
6
3
PhMgBr
5
4
11
Et2O
9
8
S
2
7
10
9
8
12
12
I
I
C4
C5
S
6
2
3
C6
4
11
7
9
8
C3
12
5
PhMgBr
10
Et2O
C2
C1
3
7
S
2
6
11
5
4
9
8
10
12
Quick test of reactivity revealed, that the closo-thiadodecaborane
moiety acts as a weak type I substituent—it does not activate the
aromatic ring towards iodination, 2-phenyl-closo-thiadodecaborane
is iodinated at the 12 position of the borane cage only, but
nitration is directed to 2 and 4 (ortho and para) positions of the
18
aromatic ring, producing 2-(4-NO2-Ph)-SB11H10 with minor admixture of
2-(2-NO2-Ph)-SB11H10. Negishi coupling, which differs from Kumada
S
6
2
S
2
3
7
3 10
11
6
4
11
5
[M(PPh3)2Cl2]
10
Et2O
M=Pd, Ni
7
12
8
4
9
12
9
8
I
5
C2
C1
C6
C3
C4
C5
reaction in the use of zinc reagents instead of magnesium ones,
proceeded normal way to change 12-iod-closo-thiadodecaborane into
12-phenyl-closo-thiadodecaborane.
2-Ph-closo-1-SB11H10: 0.904 g of closo-SB11H11 was dissolved in 10
ml of dry THF (use of diethylether lead to identical results), THF
solution of approximately fourfold excess of PhMgBr was added, and
the mixture was under nitrogen boiled under reflux for three
hours. TLC on Silufol in isohexane then indicated evolution of a
spot of RF≈0.36, round under UV detection, and protracted when
detected by both iodine wapors exposition, and reduction of AgNO3
solution spray. In addition, during the reaction there appeared an
UV visible, non reducing round spot at RF≈0.20, which is virtually
undetectable by iodine vapours, and belongs to biphenyl. The spot
of closo-SB11H11 RF≈0.54, round and reducing) had got smaller, but
retained. When left one day staying at room temperature under
nitrogen, the mixture showed no significant change in the TLC. The
mixture was dropwise added to 100 ml of diluted hydrochloric acid
(1:3), and let stay about one hour, while bubbles of gas evolved.
Then the organic phase was augmented by 50 ml of hexane, separated
from the acid, dried by MgSO4, and evaporated with small amount of
silicagel. Then it was chromatographed on a column of 100 g of
SiO2 with isohexane. 0.20 g of closo-SB11H11 was regenerated, and
0.561 g of 2-Ph-closo-SB11H10 (melting point 105—106 ºC)
acquired, which is 43% yield from the closo-SB11H11 consumed. NMR
see Table 8. MS: m/e=238 (the highest peak of the boron envelope),
smaller intensity fragments m/e=187 (envelope peak), m/e=160
(envelope peak; SB11 cage ion), and several others.
2-Ph-12-I-closo-1-SB11H9: The procedure is basically identical to
that of 2-Ph-closo-1-SB11H10 synthesis. In TLC monitoring of the
reaction, the spot of the product is hardly distinguishable from
the spot of the starting material (RF≈0.16), but its visible using
ultraviolet detection, while the starting material is not. NMR see
19
Table 9. MS: m/e=364 (the highest peak of the boron envelope),
major fragment m/e=238 (envelope peak), smaller fragments m/e=188
(envelope peak), m/e=176 (envelope peak), and several others.
2-(x-NO2-Ph)-closo-1-SB11H10 :80 mg of 2-Ph-closo-SB11H10 was
dissolved in the mixture of 25 ml of HNO3 and 10 ml of H2SO4. The
solution spontaneously warmed up; after one hour it cooled back to
the room temperature and a precipitate appeared. The mixture was
extracted by dichlormethane, the extract yielding after
evaporation 110 mg of the product, consisting of two isomers. Thin
layer chromatography on silufol plates in toluene showed two
reducing spots of RF approximatively 0.88 and 0.77 respectively.
Toluene—hexane 1:2 mixture yielded somewhat better resolution and
spots not so ahead: RF≈0.48 and 0.30 respectively, the second spot
being protracted. Attempt was made to separate them by column
chromatography on SiO2 with dichlormethane—isohexane 1:4 mixture.
The second fraction proved to be the major product, 2-(p-NO2-Ph)closo-SB11H10; to extract it completely off the column, the share
of dichlormethane in the mobile phase was finally increased to
1:2. Both fractions were crystalized from isohexane, the first one
thus yielding the minor product, 2-(o-NO2-Ph)-closo-SB11H10.
Structural studies
X-ray crystallographic study
Crystal data: H10B11SCl, a colourless block of dimensions 0.50 x
0.60 x 0.60 mm crystallizes in the monoclinic space group C2/c
with the lattice parameters a = 24.432(2), b = 14.354(4), c =
24.639(3) Å, β = 108.599(9) °, V = 8189(3) Å3, Z = 32, μ = 0.504
mm-1; 7343 reflections collected in the range 3.4° ≤ 2 ≤ 50°, 7176
reflections independent (Rint=0.028), 6043 assigned to be observed
[I > 2σ(I)], full-matrix least squares refinement against F2 with
629 parameters converged at wR(F2) = 0.0736 (R[F2 > 2σ(F2)] =
0.0248, w = 1/[σ2(Fo2) + (0.0411P)2 + 6.3952P] where P = (Fo2+2Fc2)/3)
and the max./min. residual electron density was 0.25/-0.27 eÅ-3.
Crystal data: H10B11SI, a light yellow block of dimensions 0.16 x
0.18 x 0.75 mm crystallizes in the monoclinic space group P21/n
with the lattice parameters a = 7.258(2), b = 13.260(3), c =
11.463(2) Å, β = 90.18(2) °, V = 1103.2(4) Å3, Z = 4, μ = 3.024 mm1
; 2088 reflections collected in the range 4.6° ≤ 2 ≤ 50°, 1934
reflections independent (Rint=0.020), 1808 assigned to be observed
[I > 2σ(I)], full-matrix least squares refinement against F2 with
159 parameters converged at wR(F2) = 0.0567 (R[F2 > 2σ(F2)] =
0.0216, w = 1/[σ2(Fo2) + (0.0273P)2 + 1.7095P] where P = (Fo2+2Fc2)/3)
and the max./min. residual electron density was 1.01/-0.89 eÅ-3.
Crystal data: C6H15B11S, a colourless block of dimensions 0.20 x 0.25
20
x 0.25 mm crystallizes in the monoclinic space group P21/c with the
lattice parameters a = 10.4980(2), b = 9.4510(2), c = 13.7070(3)
Å, β = 101.2760(13) °, V = 1333.71(5) Å3, Z = 4, μ = 0.205 mm-1;
20804 reflections collected in the range 4.0° ≤ 2 ≤ 55°, 3062
reflections independent (Rint=0.034), 2638 assigned to be observed
[I > 2σ(I)], full-matrix least squares refinement against F2 with
203 parameters converged at wR(F2) = 0.1424 (R[F2 > 2σ(F2)] =
0.0437, w = 1/[σ2(Fo2) + (0.0712P)2 + 0.4560P] where P = (Fo2+2Fc2)/3)
and the max./min. residual electron density was 0.32/-0.45 eÅ-3.
Crystal data: C6H14B11SI, a colourless block of dimensions 0.12 x
0.30 x 0.35 mm crystallizes in the orthorhombic space group P212121
with the lattice parameters a = 7.2400(1), b = 12.0220(2), c =
16.8320(2) Å, V = 1465.05(4) Å3, Z = 4, μ = 2.297 mm-1; 27552
reflections collected in the range 6.0° ≤ 2 ≤ 55°, 3360
reflections independent (Rint=0.043), 3276 assigned to be observed
[I > 2σ(I)], full-matrix least squares refinement against F2 with
209 parameters converged at wR(F2) = 0.0464 (R[F2 > 2σ(F2)] =
0.0189, w = 1/[σ2(Fo2) + (0.0255P)2 + 0.4466P] where P = (Fo2+2Fc2)/3)
and the max./min. residual electron density was 0.64/-0.50 eÅ-3.
Crystal data: C6H14B11NO2S (ortho isomer), a colourless block of
dimensions 0.15 x 0.25 x 0.30 mm crystallizes in the monoclinic
space group P21/n with the lattice parameters a = 10.3420(3), b =
10.6040(2), c = 13.8670(3) Å, β = 108.6060(12) °, V = 1441.26(6)
Å3, Z = 4, μ = 0.213 mm-1; 25597 reflections collected in the range
4.4° ≤ 2 ≤ 55°, 3312 reflections independent (Rint=0.034), 2751
assigned to be observed [I > 2σ(I)], full-matrix least squares
refinement against F2 with 230 parameters converged at wR(F2) =
0.1219 (R[F2 > 2σ(F2)] = 0.0387, w = 1/[σ2(Fo2) + (0.0647P)2 +
0.3833P] where P = (Fo2 + 2Fc2)/3) and the max./min. residual
electron density was 0.37/-0.41 e Å-3.
Crystal data: C6H14B11NO2S (para isomer), a colourless block of
dimensions 0.08 x 0.12 x 0.25 mm crystallizes in the orthorhombic
space group P212121 with the lattice parameters a = 6.9270(2), b =
8.9010(3), c = 23.1740(7) Å, V = 1428.85(8) Å3, Z = 4, μ = 0.215
mm-1; 15589 reflections collected in the range 6.8° ≤ 2 ≤ 50°,
2531 reflections independent (Rint=0.035), 2366 assigned to be
observed [I > 2σ(I)], full-matrix least squares refinement against
F2 with 230 parameters converged at wR(F2) = 0.0729 (R[F2 > 2σ(F2)] =
0.0305, w = 1/[σ2(Fo2) + (0.0406P)2 + 0.0999P] where P = (Fo2+2Fc2)/3)
and the max./min. residual electron density was 0.16/-0.17 eÅ-3.
21
bond/angle
SB11H11
12-Cl
12-I
S-B2 [Å]
2-Ph-12-I
2-Ph
2-o-NO2-Ph 2-p-NO2-Ph
2.053(2)
2.044(2)
2.040(18) 2.029(2)
1.999(2)
2.000(2)
2.007(2)
2.002(2)
S-B4,5 [Å]
2.010(3)
2.003(2)
2.002(2)
2.004(3)
B2-B3,6 [Å]
1.904(3)
1.901(3)
1.898(3)
1.897(3)
1.888(4)
1.883(3)
1.884(3)
1.885(3)
B4-B5 [Å]
1.879(3)
1.887(3)
1.877(3)
1.874(3)
B2-B7,11 [Å]
1.771(3)
1.768(3)
1.781(3)
1.771(3)
B3,6-B7,11 [Å]
1.766(3)
1.760(3)
1.766(3)
1.764(3)
1.765(3)
1.767(3)
1.769(3)
1.763(3)
B4,5-B8,10 [Å]
1.765(4)
1.764(3)
1.763(3)
1.762(3)
B4,5-B9 [Å]
1.762(3)
1.764(3)
1.760(3)
1.760(3)
B7-B11 [Å]
1.804(3)
1.790(3)
1.785(3)
1.782(3)
1.797(4)
1.790(3)
1.785(3)
1.786(3)
B8,10-B9 [Å]
1.799(3)
1.794(3)
1.790(3)
1.788(3)
B7,11-B12 [Å]
1.785(3)
1.789(3)
1.784(3)
1.778(3)
1.778(3)
1.782(3)
1.781(3)
1.780(3)
B9-B12 [Å]
1.779(3)
1.781(3)
1.782(3)
1.779(3)
B2-R2 [Å]
1.568(3)
1.566(3)
1.589(2)
1.572(3)
S-B3,6 [Å]
B3,6-B4,5 [Å]
B3,6-B8,10 [Å]
2.010(5) 2.003(2)
1.905(4) 1.881(3)
1.783(8) 1.760(3)
B7,11-B8,10 [Å] 1.780(11) 1.793(3)
B8,10-B12 [Å]
1.777(6) 1.778(3)
2.005(4)
1.883(5)
1.762(5)
1.793(4)
1.776(4)
B3,6-H3,6 [Å]
1.190(3) 1.058(20) 1.060(32) 1.060(30) 1.075(20) 1.095(20) 1.024(19)
B4,5-H4,5 [Å]
1.055(30) 1.085(25) 1.050(20) 1.080(20)
B7,11-H7,11 [Å]
1.035(30) 1.088(20) 1.090(20) 1.115(19)
B8,10-H8,10 [Å] 1.190(3) 1.068(20) 1.056(38) 1.080(20) 1.115(20) 1.095(20) 1.054(19)
B9-H9 [Å]
B12-X12 [Å]
S-B2-H [°]
1.030(20) 1.120(20) 1.070(20) 1.094(18)
1.190(3) 1.798(2)
2.169(3)
2.168(2)
1.120(30) 1.090(20) 1.104(19)
112.5(14) 114.4(13) 119.2(12) 113.5(12)
S-B3,6-H [°]
120.3(40) 110.2(11) 110.5(18) 111.2(15) 110.8(12) 111.8(12) 108.4(11)
S-B4,5-H [°]
109.1(15) 110.1(12) 110.3(12) 109.9(11)
B12-B7,11-H [°]
121.7(16) 123.7(12) 123.2(11) 123.2(10)
B12-B8,10-H [°] 125.3(45) 123.0(11) 124.7(18) 121.8(14) 125.0(11) 123.1(11) 123.4(11)
B12-B9-H9 [°]
123.1(13) 125.6(14) 122.9(11) 123.4(11)
Table 2: Selected X-ray determined structural parameters of SB11H11
derivatives (2-R-12-X-SB11H11) compared to the electron diffraction
data of the parent compound. The X-ray data are averaged over all
the positions that are symmetrically equivalent in solution, and
in the case of 12-Cl-SB11H10 also over all the different molecules
in the crystal cell.
22
NMR
SB11H11
2—6
7—11
12
δ(11B)
-6.67
-4.37
18.24
1
δ(1H)
J{11B—1H}
2.50
177.0
2.65
153.9
3.47
150.1
Table 3: NMR parameters of SB11H11 (11B 160.4 MHz, 1H 500 MHz; CDCl3,
ambient temperature)
12-Cl-SB11H10
2—6
7—11
12
δ(11B)
-7.95
-4.85
22.29
1
δ(1H)
J{11B—1H}
2.48
180.9
2.80
153.9
X
X
Table 4: NMR parameters of 12-Cl-SB11H10
12-Br-SB11H10
2—6
7—11
12
δ(11B)
-7.59
-4.59
15.23
1
δ(1H)
J{11B—1H}
2.54
177.0
2.91
157.8
X
X
Table 5: NMR parameters of 12-Br-SB11H10
12-I-SB11H10
2—6
7—11
12
δ(11B)
-6.91
-3.82
-0.29
1
δ(1H)
J{11B—1H}
2.63
177.0
3.08
157.8
X
X
Table 6: NMR parameters of 12-I-SB11H10
12-Ph-SB11H10
2—6
7—11
12
δ(11B)
-7.03
-4.44
26.44
1
δ(1H)
J{11B—1H}
2.63
173.2
2.95
150.1
X
X
Table 7: NMR parameters of 12-Ph-SB11H10
2-Ph-SB11H10
2
3,6
4,5
7,11
8,10
9
12
δ(11B)
7.58
-5.74
-6.15
-3.65
-4.71
-8.47
18.11
1
δ(1H)
J{11B—1H}
X
X
2.63
181.8
2.85
169.3
2.88
161.6
2.70
161.6
2.57
153.9
3.58
150.1
Table 8: NMR parameters of 2-Ph-SB11H10
23
2-Ph-12-I-SB11H9
2
3,6
4,5
7,11
8,10
9
12
δ(11B)
-0.24
-6.41
-6.41
-3.19
-4.14
-7.85
7.65
1
δ(1H)
J{11B—1H}
X
X
2.97
192.2
2.74
192.2
3.31
152.6
3.13
155.7
2.97
167.9
X
X
Table 9: NMR parameters of 2-Ph-12-I-SB11H10
2-(2-NO2-Ph)-SB11H9
2
3,6
4,5
7,11
8,10
9
12
δ(11B) δ(1H) 1J{11B—1H}
3.28 X
X
-5.62 2.67
138.5
-6.22 2.61
169.3
-3.05 2.88
150.1
-4.73 2.67
150.1
-6.22 2.67
169.3
17.85 3.55
150.1
Table 10: NMR parameters of 2-(2-NO2-Ph)-SB11H9
2-(4-NO2-Ph)-SB11H9
2
3,6
4,5
7,11
8,10
9
12
1
δ(11B)
δ(1H)
J{11B—1H}
5.61
X
X
-5.55 2.84, 2.87
150.4
-6.00
2.66
177.0
-3.51
2.89
154.1
-4.15
2.76
154.1
-7.61
2.65
150.1
18.71
3.62
146.23
Table 11: NMR parameters of 2-(4-NO2-Ph)-SB11H9
Results and Discussion
Pure closo-SB11H11 is quite stable, even on air and in contact with
water under neutral or acidic conditions; its however susceptible
to nucleophilic attack by hydroxide or flouride anions. Free
electron pair of sulphur remains unprotonized in concentrated
sulphuric acid; attempts to check its protonization by superacids
failed due to compound degradation by fluoride anions (down to
BF3).
After halogenation, only monohalogen derivatives were isolated.
Since changing silicagel to finer one lead to complete loss of
product, the reason of two and more halogenderivatives exclusion
from the purified products may be their degradation at the column,
rather than selectivity of the halogenation reactions.
As found by Císařová, all the 12 derivatives crystalize in the
monoclinic system, but their space group changes between the bromo
and iodo derivatives: X-ray structures of the chloro and iodo
derivatives were fully determined by Císařová, revealing that
24
small substituents, up to bromine, do not influence much the ball
shape of the molecule, which leads to tight packing of the
molecules into big facially centred elementary cell comprising
four symmetrically non-equivalent units, while the big iodine atom
enlarges the molecule into a rod-like shape, forming primitive
elementary cell of only one symmetrically unique molecule.
Introduction of phenyl into the 2 position leads either to
primitive monoclinic cell (2-Ph-SB11H10, 2-(2-NO2-Ph)-SB11H10) or
primitive orthorombic cell (2-Ph-12-I-SB11H9, 2-(4-NO2-Ph)-SB11H10);
there does not look like to be a simple reason for the choice
between those two space groups
These closo-thiadodecaborane derivatives were successfully used by
Všetečka to determine the dipole moments of all the compounds in
the series, confirming additivity of boron—halogen bond dipole
moments with the dipole moment of the thiaborane moiety, and
establishing thus unequivocal prove of the direction of the dipole
moment of the closo-thiadodecaborane cage. In spite of the
electronegativity difference between sulphur and boron, but in
accordance with quantum chemical calculations the sulphur atom was
proven to be at the positive end of the dipole of closothiadodecaborane.
The NMR spectra revealed little variation of boron—hydrogen
coupling constants, not exceeding the range of the experimental
error. Only the chemical shifts, both boron and hydrogen, are
influenced significantly by the substituent. Comparing the data
measured with the Hammet type relation discovered by Štíbr in the
heteroborane halogenderivatives class, we found that in the series
of closo-thiadodecaborane halogen derivatives Štíbr's relation
holds well.
Structures of the phenylderivatives synthesised were guessed on
the basis of their NMR and mass spectra, and fully determined by
Císařová using single crystal X-ray diffraction. In the structure
of 2-(2-NO2-Ph)-SB11H10 interestingly close position of one nitrogroup oxygen atom to the cage sulphur was found, suggesting
dipolar interaction of the negative oxygen with the positive
sulphur.
The difference in PhMgBr and PhZnBr reactivity towards SB11H11 is
probably due to the basicity of the reagents; attempts to react
12-I-closo-SB11H10 with phenyllithiumcuprate failed, leading to cage
degradation. The last type of reaction resembles basic degradation
of 1,2-C2B10H12 with KOH in methanol discovered by Hawthorne et al.
[35]; the ortho phenylation by PhMgBr may start with the same
nucleophilic attack as the degradation, but proceed more like the
alkoxyl addition on closo-NB11H12 reported by Paetzold et al.[92].
Absence of double substitution in one step reaction, while
subsequent phenylation is possible, suggests production of some
intermediate, which only on hydrolysis forms resulting 2-phenyl
derivatives of closo thiadodecaborane. The intermediate may be
either identical with the open nido cage structure produced from
25
closo-NB11H12[92], either common precursor to both substituted closo
cage and nido one; the degradation to lower nido skeleton in turn
may proceed either as further transformation of Paetzold's product
in basic enough environment, either as a third branch of the
common intermediate transformation. The difference of reactivity
of dicarbadodecaborane, azadodecaborane and thiadodecaborane is
unquestionably caused by the differences among the heteroatoms,
carbons donating one electron each to the inner cage orbital,
while nitrogen and sulphur being sources of both inner electrons,
both heteroatoms being in addition more electronegative than
carbon, and sulphur differing from nitrogen in stronger
electronegativity on the one hand, and larger polarizability on
the other. The question of possibility to tune reagents and
reaction conditions to obtain all three types of products for all
the heteroatoms remains open.
Dipole moments of the 12-halogen derivatives of 2 (see Table 12)
may be well regarded as addition of the group dipole moment of the
SB11 cage and the dipole moment of the boron halogen bond, both of
them having identical orientation. Sound proof of the SB11 cage
dipole orientation is thus established. The B12-X bond dipole
moments deduced from simple additivity premise are similar for
those of the halogens bonded to an alifatic carbon[93]. This
contrasts somewhat with carbaboranes explorations, showing analogy
of 9 and 12 borons in 1,2-C2B10H12 to aromatic carbon rather than
alifatic one (B-X bond dipole moments found approximately 1.5—
1.6 D), and suggests slight interaction of the polar halogen—boron
bond with the cage electronic structure, which enhances the cage
dipole moment, thus adding to the effective dipole moment of the
bond. While such an interaction may be expected both with thia and
carbaboranes, more polarizable sulphur in comparison to carbon
adds to the skeleton polarizability.
In comparison to quantum chemical calculations, apparent
underestimation of the dipole moments is seen with the DFT method,
using B3LYP potential and 6-31G* basis. MP2/6-31G* are much more
accurate, but trend similar to that observed with the chemical
shifts is seen. While the calculations, not taking into account
the SO coupling, predict boron—halogen bond dipole moment rise
from Cl to I, following the rise of the bond length, opposite
trend is actually observed, reminding thus of the so called normal
halogen dependence (NHD)[94] of chemical shifts (vide infra).
26
Experiment
MP2/6-31G*
B3LYP/6-31G*
Compound
μ [D] μ(B-X) [D] μ [D] μ(B-X) [D] μ [D] μ(B-X) [D]
SB11H11
3.64
12-Cl
12-Br
12-I
5.49
5.47
5.34
X
3.44
1.85 5.36
1.83 5.54
1.70 5.70
X
3.17
1.92 4.80
2.09 4.93
2.26 5.04
X
1.62
1.76
1.87
Table 12: Dipole moments (in Debye) of 2 and 12-X-2, X=Cl, Br, I
Calculated structural parameters (drawings of the MP2 frozen core
results in 6-31G* basis see at Fig. 9) , both MP2(fc) (Table 13)
and B3LYP (Table 14) agree very well with the experimental
parameters (Table 2) in the range of their estimated error. Both
quantum chemistry methods thus prove to be reliable and
approximately equivalent, as far as geometry is concerned. This
favours the density functional theory approach, due to its much
lesser computational demands.
(a)
(b)
(c)
(d)
Fig. 9: Calculated MP2(fc)/6-31G* geometries of closo-SB11H11 (a),
12-Cl-closo-SB11H11 (b), 12-Br-closo-SB11H11 (c), and
12-I-closo-SB11H11 (d)
bond/angle
SB11H11 12-Cl-SB11H11 12-Br-SB11H11 12-I-SB11H11
S-B2 [Å]
2.000
2.002
2.003
2.003
B2-B3 [Å]
1.876
1.875
1.876
1.875
B2-B7 [Å]
1.759
1.757
1.757
1.758
B7-B8 [Å]
1.787
1.789
1.790
1.791
B7-B12 [Å]
1.781
1.782
1.781
1.780
B2-H2 [Å]
1.188
1.187
1.188
1.188
B7-H7 [Å]
1.190
1.190
1.190
1.190
B12-X [Å]
1.190
1.783
1.951
2.183
S-B2-H2 [°]
110.0
110.1
110.2
110.2
B12-B7-H7 [°] 124.1
123.2
123.5
123.8
*
Table 13: Calculated MP2(fc)/6-31G structural parameters of
closo-SB11H11 and its halogen derivatives
27
bond/angle
S-B2 [Å]
B2-B3 [Å]
B2-B7 [Å]
B7-B8 [Å]
B7-B12 [Å]
B2-H2 [Å]
B7-H7 [Å]
B12-X [Å]
S-B2-H2 [°]
B12-B7-H7 [°]
SB11H11 12-Cl-SB11H11 12-Br-SB11H11 12-I-SB11H11
2.025
2.027
2.027
2.027
1.895
1.895
1.894
1.893
1.762
1.759
1.759
1.760
1.794
1.797
1.797
1.797
1.785
1.790
1.787
1.785
1.184
1.183
1.183
1.183
1.188
1.187
1.187
1.186
1.188
1.805
1.970
2.198
109.8
109.9
110.0
110.0
123.9
123.1
123.4
123.7
Table 14: Calculated B3LYP/6-31G* structural parameters of
closo-SB11H11 and its halogen derivatives
A comparison between calculated and experimental 11B NMR shifts
(Table 10) shows rough agreement. While calculations in 6-31G*
fail to reproduce even the relative positions of B2-6 and B7-11
signals in SB11H11, use of IGLO II basis, specially designed for NMR
calculations, in the GIAO step yields the correct pattern of the
spectra. The worst disagreement is with the experimental values is
seen in the 12 position, especially for the heavier halogens, Br
and I. In SB11H11 and 12-Cl-SB11H10, the difference may be seen as an
indicator of higher correlated computational methods being
required for proper description of the antipodal effect in
heteroboranes[34]. With Br and I the problems are undoubtedly
caused by relativistic effects playing nonnegligible role in the
electronic structure of heavy atoms. These effects are well known
to outweight the electronegativity of the halogens and cause
significant decrease of chemical shifts of atoms bound halogens
with increasing atom number of the halogen—so called normal
halogen dependence (NHD)[94]. Simple use of pseudopotentials,
approximating relativistic energies, was found insufficient for
the NMR description.
28
compound position expt. calc. 1 calc. 2 calc. 3 calc. 4a calc 5a
B12
18.2
21
22.5
21.2
B7—11
B2—6
-4.4
-6.7
-5.6
-5.2
-4.4
-4.8
-6.1
-7.2
12-Cl-2
B12
B7—11
B2—6
22.3
-4.9
-8
27.6
-5.6
-6.8
28.7
-4.3
-6.3
12-Br-2
B12
B7—11
B2—6
15.2
-4.6
-7.6
33.1
-4.1
-6.1
12-I-2
B12
B7—11
B2—6
-0.3
-3.8
-6.9
29.6
-3.8
-5.5
SB11H11
18.8
19.1
27.6
-6.8
-8.8
22.3
20.6
29.1
-3.9
-5.8
29.1
-6.3
-8.4
23
12.9
28.6
-2.8
-5.2
30.2
-5.4
-7.7
22.4
-7.5
Table 15: Experimental and computed NMR chemical shifts of closoSB11H11 and its halogenderivatives:
Calc. 1: GIAO SCF//MP2/6-31G*, ECP for Br, I
Calc. 2: GIAO SCF/IGLO II//MP2/6-31G*, ECP for Br, I
Calc. 3: GIAO B3LYP/IGLO II//B3LYP/6-31G*, ECP for Br, I
Calc. 4Error: Reference source not found: SOS-DFPT(IGLO)/IGLO II//
MP2/6-31G*a
Calc. 5Error: Reference source not found: SOS-DFPT(IGLO)/IGLO II
with spin-orbital couplinga , MP2/6-31G* geometry
a
results of calculations 4, 5 provided by M. Kaupp
The main relativistic effect determining the NMR parameters is
spin-orbital (SO) coupling. As electrons are charged particles,
their motion in orbitals with nonzero angular momentum generates
magnetic field. When the electrons reach relativistic velocities
in heavy atoms, their orbital magnetic momentum becomes big enough
to couple signifficantly with their spin magnetic momentum. That
not only affects the energies of such electrons, but has even
stronger impact on the electronic structure changes in the
presence of external magnetic field and on the interaction of the
electrons with the nuclear magnetic momentum. Computational
methods to take SO coupling into account are in developement, and
results of their application, kindly provided by M. Kaupp (see
Table 15) prove, that SO coupling inclusion substantially improves
the agreement with experimental data. While the improvement in the
case of SB11H11 and 12-Cl-SB11H10 is independent of SO-coupling
inclusion in the calculations, and either is a matter of better
luck or demonstrates superiority of the experimental NMR code,
accounting better for electron correlation effects, the change of
the results for 12-Br-SB11H10 and 12-I-SB11H10 is remarkable, SO
coupling inclusion repairing the discrepancy between experiment
and theory to great extent (see Fig. 10). This is in concert with
previous SO coupling explorations of Kaupp et al.[95]
29
35
30
δ(11B)
25
20
15
10
5
0
-5
-10
H
Cl
Br
I
halogen
experimental values
HF//MP2/6-31G*
HF/IGLO-II//MP2/6-31G*
B3LYP/IGLO-II//6-31G*
SOS-DFPT
SOS-DFPT with SO
Fig. 10: Normal halogen dependence of the 11B NMR
chemical shifts of the boron 12 in the halogen
derivatives of closo-SB11H11: on the way to iodine
all the calculations ignoring spin-orbital
coupling diverge significantly from the
experimental values.
The influence of the substituent on the NMR parameters was studied
extensively for many different classes of boranes and
heteroboranes[34]. Mostly chemical shifts were targeted by that
effort, and tables 3—11 show that in the case of the closo-SB11H11
derivatives we should focus the shifts too; the boron—hydrogen
coupling constants vary only little amongst different substitution
derivatives, especially in comparison to the experimental error
(see the spectra presented in the supplementary materials), and no
significant trend is seen in their variation. The situation of the
coupling constants in the thiadodecaborane series appears to be
even worse than in the series of substituted
dicarbadodecaboranes[58].
Major contribution to the substituent effect on the NMR chemical
shifts in the icosahedral borohydride class was done by Janoušek
et al.[96], comparing differences of the 11B chemical shifts of Chalogenated closo-CB11H12- from the shifts of the parent compound
with previously collected similar data series for B12 substituted
closo-CB11H12-, halogenated closo-B12H122-, and the three isomeric
30
closo-C2B10H12, and correlating the chemical shift differences with
the electronegativities of the halogens. While the correlation
found strongly suggested the halogen electronegativity to be the
major source of the chemical shifts change, even better
correlation was found by Štíbr, inspecting the new SB11H11
derivatives series, amongst the data series themselves, especially
for the substituted (ipso) positions[97]. In the Table 16 the data
for C5v compounds from the work of Janoušek et al.[96] are
summarized along with the relevant parameters of the closo-SB11H11.
Series
1-X-CB11H11-
1-X-B12H112-
12-X-CB11H11-
12-X-SB11H10
position \ X F
Cl
Br
I
ipso
61.1 18.3 -1.9 -44.4
ortho
-0.3
3.8
4.2
5.3
meta
-3.4 -0.3
0.2
1.2
para
-9.8 -4.9 -3.6
-1.3
ipso
25.5 12.5
7.1
-6.0
ortho
-1.4
0.5
1.0
1.6
meta
-3.2 -1.3 -0.6
0.1
para
-8.7 -4.9 -3.6
-1.6
ipso
21.0 10.3
4.4 -11.2
ortho
-1.2
0.4
1.0
1.3
meta
-2.5 -1.2 -0.2
-0.1
ipso
X
4.05 -3.01 -18.53
ortho
X -0.48 -0.22
0.55
meta
X -1.28 -0.92 -0.24
Table 16: Differences of halogen substituted icosahedral boranes
chemical shifts from the shifts of the parent compounds (in ppm)
Graphs at Fig. 11 show Štíbr's relation for the four individual
positions in the icosahedron. The data show almost exactly linear
dependence, with the fluorine derivatives numbers (not available
in the presently obtained SB11 series) falling furthest off the
line. Interestingly, inclusion of the parent compounds (X=H, Δδ=0
by definition) would break the linear relation of the series
totally. Since Štíbr's relation looks too good and too general to
be totally random, the hydrogen standing out may suggest (at
least) two-parametric dependence of the chemical shifts upon the
substituent, with halogens having (at least) one parameter
(roughly) fixed or linearly dependent. Thus the deviation of
fluorine derivatives data from the lines of the other halogen
derivatives may be caused by fluorine being partially similar to
hydrogen. Proper extension of Štíbr's relation beyond halogens,
explanation of its origin and of the hydrogen anomaly will
probably require multicomponent analysis of much more extensive
data.
31
30
25
20
Δδ [ppm]
15
10
5
a)
0
-5
-10
-15
-20
-45 -40 -35 -30 -25 -20 -15 -10 -5
0
5
10
15 20
25 30
35 40 45 50 55 60
65
Δδ(13C) in 1-X-CB11H12- [ppm]
1-X-B12H112-
12-X-CB11H11-
12-X-SB11H10
6
5
b)
Δδ [ppm]
4
3
2
1
0
-1
-2
-45 -40 -35 -30 -25 -20 -15 -10 -5
0
5
10 15 20 25
30 35 40 45 50 55 60 65
Δδ(13C) in 1-X-CB11H12- [ppm]
1-X-B12H112-
12-X-CB11H11-
12-X-SB11H10
12-X-SB11H10
32
2
Δδ [ppm]
1
0
-1
c)
-2
-3
-4
-45 -40 -35 -30 -25 -20 -15 -10 -5
0
5
10 15
20 25 30 35 40 45 50 55 60 65
Δδ( C) in 1-X-CB11H12- [ppm]
13
1-X-B12H112-
12-X-CB11H11-
12-X-SB11H10
12-X-SB11H10
-2
-3
Δδ [ppm]
-4
d)
-5
-6
-7
-8
-9
-10
-45 -40 -35 -30 -25 -20 -15 -10 -5
0
5
10 15 20 25 30 35 40 45 50 55 60 65
Δδ( C) in 1-X-CB11H12- [ppm]
13
1-X-CB11H11-
1-X-B12H112-
Fig. 11: Štíbr's relation — 11B NMR chemical shift differences
caused by halogen substitution in icosahedral boron cages
33
correlated with the appropriate 13C chemical shift differences in
the C-halogenated closo-CB11H12- anion. a) the substituted (ipso)
atom; b) the nearest neighbours — ortho position; c) the meta
position; d) the directly opposite (para) atom.
References
[1] Greenwood N. N., Earnshaw A.: Chemistry of the elements,
Pergamon Press, London, 1984
[2] Jones F., Taylor R. L.: J. Chem. Soc., Trans. 39, 213 (1881)
[3] Stock A.: Hydrides of Boron and Silicon, Cornell Univ. Press,
Ithaca, New York, 1933
[4] Stock A., Massenez C.: Chem. Ber. 45, 3539 (1912)
[5] Dilthey W.: Angew. Chem. 34, 596 (1921)
[6] Hedberg K., Schomaker V.: J. Am. Chem. Soc. 73, 1482 (1951)
[7] Brown H. C., Schlesinger H. I., Burg A. B.: J. Am. Chem. Soc.
61, 673 (1939)
[8] Schlesinger H. I., Brown H. C., Gilbreath J. R., Katz J. J.:
J. Am. Chem. Soc. 75, 195 (1953)
[9] Schlesinger H. I., Brown H. C., Hyde E. K.: J. Am. Chem. Soc.
75, 209 (1953)
[10] Schlesinger H. I., Brown H. C., Hoekstra H. R., Rapp L. R.:
J. Am. Chem. Soc. 75, 199 (1953)
[11] Schlesinger H. I., Brown H. C., Finholt A. E.: J. Am. Chem.
Soc. 75, 205 (1953)
[12] Brown H. C.: Boranes in Organic Chemistry, Cornell University
Press, Ithaca and London, 1972
[13] Kasper J. S., Lucht C. M., Harker D.: Acta Crystallogr. 3,
436 (1950)
[14] Hedberg K., Jones M. E., Schomaker V.: J. Am. Chem. Soc. 73,
3538 (1951)
[15] Dulmage W. J., Lipscomb W. N.: J. Am. Chem. Soc. 73, 3539
(1951)
[16] Dulmage W. J., Lipscomb W. N.: Acta Crystallogr. 5, 260
(1952)
[17] Perry D. E.: Missiles, Rockets 3, 31 (1958)
[18] Michajlov B. M.: Chimija borovodorodov, Nauka, Moskva, 1967
[19] Pitochelli A. R., Hawthorne M. F.: J. Am. Chem. Soc. 82, 3228
(1960)
[20] Miller H. C., Miller N. E., Muetterties E. L.: J. Am. Chem.
Soc. 85, 3885 (1963)
[21] Miller H. C., Miller N. E., Muetterties E. L.: Inorg. Chem.
3, 1456 (1964)
[22] Longuet-Higgins H. C., Roberts M. V.: Proc. Royal Soc.
(London) A230, 110 (1955)
[23] Longuet-Higgins H. C.: J. Chem. Phys. 46, 268 (1949)
[24] Longuet-Higgins H. C.: J. Roy. Inst. Chem. 77, 179 (1953)
[25] Ebergardt W. H., Crawford B. Jr., Lipscomb W. N.: J. Chem.
Phys. 22, (1954)
[26] Dickerson R. E., Lipscomb W. N.: J. Chem. Phys. 27, 212
(1957)
[27] Lipscomb W. N., Advances in theoretical studies of boron
34
hydrides and carboranes, in: Muetterties E. L. (ed.): Boron
Hydride Chemistry, chap. 2, p. 30, Academic Press, New York 1975
[28] Hoffmann R., Lipscomb W. N.: J. Chem. Phys. 36, 2179 (1962)
[29] Hoffmann R., Lipscomb W. N.: J. Chem. Phys. 37, 520 (1962)
[30] Aihara J.: J. Am. Chem. Soc. 100, 3339 (1978)
[31] King R. B.: Chem. Rev. 101, 1119 (2001)
[32] Schleyer P. v. R.: Chem. Rev. 101, 1115 (2001)
[33] Wade K.: Adv. Inorg. Chem. Radiochem. 18, 1 (1976)
[34] Heřmánek S.: Chem. Rev. 92, 325 (1992)
[35] Wiesboeck R. A., Hawthorne M. F.: J. Am. Chem. Soc. 86, 1642
(1964)
[36] Dunks G. B., McKown M. M., Hawthorne M. F.: J. Am. Chem. Soc.
93, 2541 (1971)
[37] Janoušek Z., Fusek J., Štíbr B.: J. Chem. Soc. Dalton Trans.
1992, 2649
[38] Fox M. A., Wade K.: Pure Appl. Chem. 75, 1315 (2003)
[39] Elian M., Hoffman R.: Inorg. Chem. 14, 1058 (1975)
[40] Grimes R. N.: Carboranes, Academic Press, New York, 1970
[41] Driess M. (ed.), Nöth H. (ed.): Molecular Clusters of the
Main Group Elements, Wiley-VCH, Weinheim, 2004
[42] Paetzold P.: Pure & Appl. Chem. 63, 345 (1991)
[43] Štíbr B.: Collect. Czech. Chem. Commun. 67, 843 (2002)
[44] Hertler W., Klanberg F., Muetterties L.: Inorg. Chem. 6, 1696
(1967)
[45] Pretzer W. R., Rudolph R. W.: J. Am. Chem. Soc. 98, 1441
(1976)
[46] Holub J., Štíbr B., Kennedy J. D., Thornt-Pett M., Jelínek
T., Plešek J.: Inorg. Chem. 33, 4545 (1994)
[47] Štíbr B., Holub J., Jelínek T., Fontaine X. L. R., Fusek J.,
Kennedy J. D., Thornton-Pett M.: J. Chem. Soc. Dalton Trans. 1996,
1741
[48] Plešek J., Heřmánek S.: J. Chem. Soc. Chem. Commun. 1975, 127
[49] Kang S., Sneddon L.: Inorg. Chem. 27, 3298 (1988)
[50] Smith W., Meneghelli B., Thompson D., Klymko P., McClure N.,
Bower M., Rudolph R.: Inorg. Chem. 16, 3008 (1977)
[51] Hnyk D., Vajda E., Bühl M., Schleyer P. v. R.: Inorg. Chem.
31, 2464 (1992)
[52] Møllendal H., Samdal S., Holub J., Hnyk D.: Inorg. Chem. 42,
3043 (2003)
[53] Tucker P. M., Onak T.: J. Am. Chem. Soc. 91, 6869 (1969)
[54] Tucker P. M., Onak T., Leach J. B.: Inorg. Chem. 9, 1430
(1970)
55: Heřmánek S., Plešek J., Štíbr B., Abstr. no. 38, 1974
[56] Heřmánek S., Gregor V., Štíbr B., Plešek J., Janoušek Z.,
Antonovich V. A.: Collect. Czech. Chem. Commun. 41, 1492 (1976)
[57] Teixidor F., Viñas C., Rudolph R. W.: Inorg. Chem. 25, 3339
(1986)
[58] Heřmánek S., Macháček J., Fusek J., Blechta V., Importance of
11
B—1H Coupling Constants in Assigning the 11B-Signals, in: Casanova,
J. (ed.): The Borane, Carborane, Carbocation Continuum, chap. , p.
367, John Wiley and Sons, Canada 1998
35
[59] Shriver D. F., Drezdon M. A.: Manipulation of Air Sensitive
Compounds, Wiley, New York, 1986
[60] Altomore A., Burla M. C., Camalli M., Cascarano G.,
Giacovazzo C., Guagliardi A., Molinerni A. G. G., Polidori G.,
Spagna R.: J. Appl. Crystalogr. 32, 115 (1999)
[61] Sheldrick G. M.: SHELX97, Program for Crystal Structure
Refinement from Diffraction Data, University of Gőttingen
(Germany) 1997
[62] Všetečka V.: Chem. Listy 89, 256 (1995)
[63] Guggenheim E. A.: Trans. Faraday Soc. 45, 714 (1949)
[64] Smith J. W.: Trans. Faraday Soc. 46, 256 (1950)
[65] Frisch M. J., Trucks G. W., Schlegel H. B., Gill P. M. W.,
Johnson B. G., Robb M. A., Cheeseman J. R., Keith T., Petersson G.
A., Montgomery J. A., Raghavachari K., Al-Laham, M. A., Zakrzewski
V. G., Ortiz J. V., Foresman J. B., Cioslowski J., Stefanov B. B.,
Nanayakkara A., Challacombe M., Peng C. Y., Ayala P. Y., Chen W.,
Wong M. W., Andres J. L., Replogle E. S., Gomperts R., Martin R.
L., Fox D. J., Binkley J. S., Defrees D. J., Baker J., Stewart J.
P., Head-Gordon M., Gonzalez C., Pople J. A.: Gaussian 94,
Revision D.4, Gaussian Inc., Pittsburgh PA, 1995
[66] Møller C., Plesset M. S.: Phys. Rev. 46, 618 (1934)
[67] Hariharan P. C., Pople J. A.: Theoret. Chimica Acta 28, 213
(1973)
[68] Dill J. D., Pople J. A.: J. Chem. Phys. 62, 2921 (1975)
[69] Francl M. M., Petro W. J., Hehre W. J., Binkley J. S.,
Gordon M. S.: J. Chem. Phys. 77, 3654 (1982)
[70] Frisch M. J., Pople J. A., Binkley J. S.: J. Chem. Phys. 80,
3265 (1984)
[71] Bergner A., Dolg M., Küchle W., Stoll H., Preuss H.: Mol.
Phys. 80, 1431 (1993)
[72] Roothan C. C. J.: Rev. Mod. Phys. 23, 69 (1951)
[73] London F.: J. Phys. Radium, Paris 8, 397 (1937)
[74] Ditchfield R.: Mol. Phys. 27, 789 (1974)
[75] Wolinski K., Hilton J. F., Pulay P.: J. Am. Chem. Soc. 112,
8251 (1990)
[76] W. Kutzelnigg, U. Fleischer, M. Schindler: The IGLO-Method:
Ab Initio Calculation and Interpretation of NMR Chemical Shifts
and Magnetic Susceptibilities, Vol. 23, Springer-Verlag,
Heidelberg, 1990
[77] Kohn W., Sham L. J.: Physical Review 140, A1133 (1965)
[78] Becke A. D.: J. Chem. Phys. 98, 5648 (1993)
[79] Lee C., Yang W., Parr R. G.: Physical Review B 37, 785 (1988)
[80] Malkin V. G., Malkina O. L., Malkina L. A., Eriksson L. A.,
Salahub D. R., in: Politzer P., Seminario J. M. (ed.): Theoretical
and computational chemistry, Vol. 2, Elsevier, Amsterdam 1995
[81] Malkin V. G., Malkina O. L., Casida M. E., Salahub D. R.: J.
Am. Chem. Soc. 116, 5898 (1994)
[82] Kutzelnigg W.: Isr. J. Chem. 19, 193 (1980)
[83] Schindler M., Kutzelnigg W.: J. Chem. Phys. 76, 1919 (1982)
[84] Salahub D. R., Fournier R., Mlynarski P., Papai I., St-Amant
A., Ushio J., in: Labanowski J. K., Andzelm J. W. (ed.): Density
36
functional methods in chemistry, p. 77, Springer, Berlin 1991
[85] Malkin V. G., Malkina O. L., Salahub D. R.: Chem. Phys. Lett.
261, 335 (1996)
[86] Holub J.: personal communication
[87] Plešek J.: personal communication
[88] Štíbr B., Janoušek Z., Plešek J., Jelínek T., Heřmánek S.:
Collect. Czech. Chem. Commun. 52, 103 (1987)
[89] Štíbr B.: personal communication
[90] Fox M. A.: Icosahedral Carborane Derivatives, University of
Durham 1991
[91] Tamao K., Kiso Y., Sumitani K., Kumada M.: J. Am. Chem. Soc.
94, 4374 (1972)
[92] Paetzold P., Mülller J., Meyer F., Hansen H.-P., Schneider
L.: Pure & Appl. Chem. 66, 255 (1994)
[93] Exner O.: Dipole Moments in Organic Chemistry, Thieme
Publishers, Stuttgart, 1975
[94] Kidd R. G.: Ann. Rep. NMR Spectrosc. 23, 85 (1991)
[95] Kaupp M., Malkina O. L., Malkin V. G.: Chem. Phys. Lett. 265,
55 (1997)
[96] Janoušek Z., Hilton C. L., Schreiber P. J., Michl J.:
Collect. Czech Chem. Comm. 67, 1025 (2002)
[97] Macháček J., Plešek J., Holub J., Hnyk D., Všetečka V.,
Císařová I., Kaupp M., Štíbr B.: in preparation
37
Supplement: Selected NMR and mass spectra
The basic member of the series cannot be omitted; however, since
it is the best known of the compounds, only boron NMR spectra are
presented:
a)
b)
Supp. 1: 1H decoupled (a) and coupled (b)
closo- SB11H11
11
B NMR spectra of
38
Using the chlorine derivative to demonstrate various kinds of NMR
spectra will be slightly more interesting:
a)
b)
Supp. 2: 1H decoupled (a) and coupled (b)
12-Cl-closo- SB11H10
11
B NMR spectra of
39
a)
b)
Supp. 3: 11B decoupled (a) and coupled (b) 1H NMR spectra of
12-Cl-closo- SB11H10
Impact of boron coupling on proton spectra favours the use of
selective decoupling technique to assign the hydrogen atoms to the
borons they are bonded to.
40
Supp. 4: selective 11B decoupling of 1H NMR spectra of
12-Cl-closo-SB11H10
The assignment of boron signals to the individual positions in the
cage is significantly eased by correlated spectroscopy:
Supp. 5: 1H decoupled homonuclear correlated
spectrum of 12-Cl-closo- SB11H10
B NMR
11
GC-MS analysis allows straightforward comparison of pure
41
12-Cl-closo-SB11H10 to the mixture of positional isomers:
a)
b)
Supp. 6: GC-MS of 12-Cl-SB11H10 (a) and an isomer mixture (b);
presence of the parent SB11H11 is seen in both cases
NMR spectra of the mixture are, however, hard to decipher, due to
small differences among multiple signals and large signal width.
42
a)
b)
Supp. 7: 1H decoupled (a) and coupled (b)
mixture of 12- and 7-Cl-closo-SB11H10
11
B NMR spectra of the
Signal at -13.5 ppm nevertheless can be attributed to the
antipodal shift caused by the substituted boron, and the absence
of crosspeak between this signal and 18.7 ppm of the B12 in
otherwise not much legible correlated boron spectrum identifies 7chlor derivative, the antipodal atom of the substituted one being
thus located at the upper rim of the cage.
43
Supp. 8: 11B—11B correlated NMR spectrum of the 12- and
7-Cl-closo- SB11H10 mixture
Thus NMR identifies the products, while GC-MS (Supp. 6b) affords
quantitative analysis of their mixture (Supp. 9).
No. Tret
Scan Peak Height Peak Area Area Percent
1
9:46
586
102871
163002
5.647
2
12:03 723
683493
979577
33.935
3
12:14 734
1200252
1744093
60.419
Supp. 9: quantitative GC-MS analysis of the 12- and
7-Cl-closo-SB11H10 mixture
To complete the series, 11B NMR spectra of 12-Br-, 12-I-, and 12phenyl-closo-SB11H10 are presented:
44
a)
b)
Supp. 10: 1H decoupled (a) and coupled (b)
12-Br-closo- SB11H10
11
B NMR spectra of
45
a)
b)
Supp. 11: 1H decoupled (a) and coupled (b)
12-I-closo-SB11H10
11
B NMR spectra of
46
a)
b)
Supp. 12: 1H decoupled (a) and coupled (b)
12-Ph-closo- SB11H10
11
B NMR spectra of
For the parent thiadodecaborane and all the halogenderivatives
correlated 11B—1H spectra with coupled protons were measured to
determine the 11B—1H coupling constants as precisely as possible.
The breadth of signals, however, lowers the precision, and
47
prevents resolution of signals in more complicated cases just the
same way, as its affected in simple coupled 11B spectra:
48
a)
b)
49
c)
d)
Supp. 13: 11B—1H correlated spectra with coupled protons for
closo- SB11H11 (a) and its 12-Cl (b), Br (c, relevant traces of the
two-dimensional spectrum are shown) and I (d) derivatives
The formation of 2-Ph-12-I-SB11H9 instead of iodine exchange was
discovered in the mass spectra of the product, while the fact,
that the substitution takes place at the upper rim of the cage
became apparent from the NMR spectra of the parent compound
phenylation product. The atom antipodal to the phenylated position
50
(-8.4 ppm) has crosspeak with B12 (18.1 ppm).
Supp. 14: mass spectrum of 2-Ph-12-I-SB11H9—simultaneous
presence of phenyl and iodine in the molecule revealed
51
a)
b)
52
c)
Supp. 15: 1H decoupled (a) and coupled (b) 11B, and 1H decoupled
11
B correlated NMR spectra of 2-Ph-closo-SB11H10
B—
11
The difference between ortho and para nitrophenyl on the
thiadodecaborane cage is apparent, but does not help to determine,
what isomers they are (Supp. 16).
53
a)
b)
Supp. 16: 1H decoupled 11B NMR spectra of 2-(2-NO2-Ph)- (a) and
2-(4-NO2-Ph)-closo- SB11H10
54
a)
b)
Supp. 17: 1H NMR spectra (coupled in one picture with
of 2-(2-NO2-Ph)- (a) and 2-(4-NO2-Ph)-SB11H10
B decoupled)
11
The 1H NMR spectra (Supp. 17) are of no more help, since phenyl
hydrogens should indicate the benzene ring substitution, but their
spectrum is of the second order, and moreover the interaction with
55
the thiadodecaborane skeleton breaks the symmetry of para
substituted benzene ring. What looks like a simple spectrum of
symmetrically substituted benzene ring, belongs actually to the
ortho isomer, and is a product of a coincidence of higher number
of peaks (Supp. 18). Thus the isomers had to be identified by Xray crystallography.
Supp. 18: phenyl part of the 1H NMR spectrum of
2-(2-NO2-Ph)-closo- SB11H10
56
Corrected references:
Møllendal H., Samdal S., Holub J., Hnyk D.: Inorg. Chem. 42, 3043
(2003)
Frisch M. J., Trucks G. W., Schlegel H. B., Gill P. M. W., Johnson
B. G., Robb M. A., Cheeseman J. R., Keith T., Petersson G. A.,
Montgomery J. A., Raghavachari K., Al-Laham, M. A., Zakrzewski V.
G., Ortiz J. V., Foresman J. B., Cioslowski J., Stefanov B. B.,
Nanayakkara A., Challacombe M., Peng C. Y., Ayala P. Y., Chen W.,
Wong M. W., Andres J. L., Replogle E. S., Gomperts R., Martin R.
L., Fox D. J., Binkley J. S., Defrees D. J., Baker J., Stewart J.
P., Head-Gordon M., Gonzalez C., Pople J. A.: Gaussian 94,
Revision D.4, Gaussian Inc., Pittsburgh PA, 1995.
Møller C., Plesset M. S.: Phys. Rev. 46, 618 (1934)
Teixidor F., Viñas C., Rudolph R. W.: Inorg. Chem. 25, 3339 (1986)
57
Contents
Introduction
1
The state of the art
8
closo-thiadodecaborane synthesis
NMR spectroscopy of boranes
Experimental section
8
10
12
General procedures
12
closo-thiadodecaborane
13
12-halogenderivatives of closo-thiadodecaborane
15
Phenyl derivatives of closo-thiadodecaborane
18
Structural studies
20
X-ray crystallographic study
20
NMR
22
Results and Discussion
24
References
33
Supplement: Selected NMR and mass spectra
37
58
Jan Macháček
Synthesis and physical properties of closothiadodecaborane derivatives
Submitted as a PhD thesis at the
Faculty of Natural Sciences of the
Charles University,
Prague
2005
Supervisor: Doc. RNDr. Václav Všetečka, CSc.
Consultants: Ing. Bohumil Štíbr, DrSc.
RNDr. Drahomír Hnyk, CSc.
and late
Doc. Ing. Stanislav Heřmánek, CSc.
to whom this work is dedicated